CN115021283A - Energy-storage-free photovoltaic voltage type control method and system - Google Patents
Energy-storage-free photovoltaic voltage type control method and system Download PDFInfo
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- H—ELECTRICITY
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- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
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- H—ELECTRICITY
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- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J3/00—Circuit arrangements for ac mains or ac distribution networks
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- H02J2300/22—The renewable source being solar energy
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- H02J2300/26—The renewable source being solar energy of photovoltaic origin involving maximum power point tracking control for photovoltaic sources
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Abstract
The invention discloses a non-energy-storage photovoltaic voltage type control method and a system, wherein a rear-stage inverter is adopted to realize double droop control of voltage and frequency at a direct current side; detecting the working mode of the photovoltaic inverter, and obtaining a photovoltaic working mode value FlagMPP and the motion condition of the current photovoltaic working point according to the sampled photovoltaic output voltage and the photovoltaic output power; determining the photovoltaic output voltage corresponding to the maximum power point according to the motion condition of the current photovoltaic working point; according to the photovoltaic output voltage corresponding to the maximum power point and the photovoltaic port voltage control instruction value, the control strategies of the non-energy-storage photovoltaic inverter under two modes that the load demand power is greater than the photovoltaic maximum power and the load demand power is smaller than the photovoltaic maximum power are achieved by utilizing the PWM duty ratio signal. The reasonable distribution of the power of each inverter in the photovoltaic island microgrid, the active support of the voltage frequency of the alternating current bus and the simultaneous processing of the power disturbance from the two sides of the source load by the photovoltaic inverter are realized.
Description
Technical Field
The invention belongs to the technical field of new energy power generation and converter control, and particularly relates to a control method and system of a non-energy-storage photovoltaic voltage type.
Background
In new energy power generation technology, photovoltaic power generation is widely distributed and easy to use, so that the photovoltaic power generation is concerned. However, the high reliance of photovoltaic power generation on electrical grids, energy storage and energy management systems severely limits their development. The photovoltaic inverter is very important in the utilization of solar energy, the photovoltaic array converts the solar energy into electric energy, and the inverter controls the output of the photovoltaic array to meet the load requirement, so that the photovoltaic array and the converter can be reasonably controlled to better utilize the solar energy.
In order to improve the utilization rate of solar energy of the photovoltaic array, the converter is controlled by taking the maximum power output by the photovoltaic array in a specific environment as a target, but in an island microgrid, the principle of matching with source load power is contrary, and meanwhile, in order to enable the photovoltaic inverter to actively support the voltage and the frequency of an alternating current bus, MPP operation is gradually replaced by a more flexible active power control method. Active power control can match the photovoltaic output power to the load demand by controlling the converter, not needing to operate at the maximum power point but regulating the photovoltaic output power by tracking the load demand.
However, when the photovoltaic output power fluctuates greatly and sudden load changes occur, the photovoltaic system may not meet the power demand of the load and thus be disconnected from the load, which is a serious waste for the photovoltaic system with the power generation capacity. In such a power shortage situation, a corresponding control method is required to switch the operation mode of the inverter, and this operation has a great influence on the photovoltaic inverter controlled by the voltage source.
Disclosure of Invention
The technical problem to be solved by the present invention is to provide a method and a system for controlling a non-energy-storage photovoltaic voltage type, aiming at the defects in the prior art, so as to realize reasonable distribution of power of each inverter in a photovoltaic island microgrid, actively support the voltage frequency of an alternating current bus, and enable a photovoltaic inverter to simultaneously process power disturbances from two sides of a source load.
The invention adopts the following technical scheme:
a control method of a non-energy-storage photovoltaic voltage type comprises the following steps:
s1, outputting voltage u according to d and q axes reference of inverter d_ref 、u q_ref Obtaining modulation wave M under d and q axes by utilizing double closed-loop control of voltage and current d 、M q Then, the inverter three-phase modulation wave M is obtained by utilizing the inverter reference output voltage phase angle theta and through coordinate transformation a 、M b 、M c Then converting the voltage into a PWM duty ratio signal, and realizing double droop control of voltage and frequency at the direct current side by adopting a rear-stage inverter;
s2, detecting the working mode of the photovoltaic inverter and outputting the voltage u according to the sampled photovoltaic pv And the photovoltaic output power p pv Obtaining a photovoltaic working mode value flag MPP and the motion condition of the current photovoltaic working point;
s3, according to the movement situation of the current photovoltaic working point obtained in the step S2, if the load needs power P L Greater than the maximum photovoltaic power P MPP The photovoltaic inverter is enabled to work at the maximum power point through MPPT control, and the voltage of a photovoltaic port is controlled to be a command value u pv_ref The photovoltaic output voltage is used as the maximum power point; if the load demands power P L Less than the maximum photovoltaic power P MPP Switching the working mode according to the instruction value p of the output power of the photovoltaic array pv,ref Obtaining the photovoltaic output power p pv And calculating a photovoltaic port voltage control command value u by using the photovoltaic working mode value Flag pv_ref The photovoltaic output voltage is used as the maximum power point;
s4, obtaining the photovoltaic output voltage u corresponding to the maximum power point according to the step S3 pv Photovoltaic port voltage control command value u pv_ref And utilizing the PWM duty ratio signal obtained in the step S1 to realize the power P required by the non-energy-storage photovoltaic inverter under the load L Greater than the maximum photovoltaic power P MPP And the load demand power P L Less than the maximum photovoltaic power P MPP Control strategies in two modes.
Specifically, step S1 specifically includes:
s101, determining a direct-current side voltage reference value U of the inverter 0 Sag factor k d Virtual inertia J, synchronous angular frequency w ref Dc side capacitor C of inverter 0 And calculating a relation coefficient G between the input power of the photovoltaic array to the inverter and the DC side voltage of the inverter according to the relation coefficient G u And the relation coefficient G between the DC side voltage and the output frequency of the inverter w ；
S102, obtaining a DC side voltage reference value U of the inverter 0 And sampling the DC side voltage u of the inverter 0 Will u 0 And U 0 Making difference by using a relation coefficient G between the input power of the photovoltaic array to the inverter and the DC side voltage of the inverter u And the relation coefficient G between the DC side voltage and the output frequency of the inverter w And calculating to obtain a photovoltaic array output power instruction value p pv_ref Phase angle theta with the reference output voltage of the inverter;
s103, sampling the output voltage u of the inverter port abc Output current i abc Obtaining d-and q-axis voltages u through coordinate transformation d 、u q And a current i d 、i q Then, calculating to obtain real-time output reactive power Q of the inverter;
s104, according to the reactive power Q and the droop coefficient k d The rated voltage amplitude U of the alternating current bus of the inverter and the virtual impedance link are calculated to obtain the output reference voltage U of the d and q axes of the inverter d_ref 、u q_ref ；
S105, obtaining d-axis and q-axis reference output voltages u of the inverter d_ref 、u q_ref Obtaining modulation wave M under d and q axes by utilizing voltage current double closed-loop control d 、M q Then, the inverter three-phase modulation wave M is obtained by coordinate transformation by using the inverter reference output voltage phase angle theta obtained in the step S104 a 、M b 、M c And then converted into a PWM duty signal.
Further, in step S104, the inverter outputs reference voltage u on d and q axes d_ref 、u q_ref Comprises the following steps:
wherein L is v Is virtual impedance, U is rated voltage amplitude of AC bus of inverter, Q is reactive power, k d Is the sag factor, w ref For synchronous angular frequency, i d 、i q And outputting the value of the current under the dq synchronous rotation coordinate system for the inverter.
Further, in step S105, the PWM duty signal is:
wherein M is a 、M b 、M c For inverter three-phase modulated waves, θ is, M d 、M q A modulation command value is generated for the d-axis current inner loop.
Specifically, in step S2, the photovoltaic operating mode value FlagMPP specifically includes:
wherein u is old And p old Respectively the photovoltaic port voltage and the photovoltaic power u at the previous moment pv For sampling the output voltage of the photovoltaic cell, p pv The photovoltaic output power.
Further, detecting the operating mode of the photovoltaic inverter specifically includes:
s201, sampling by the photovoltaic system to obtain the output voltage u of the current photovoltaic array pv Current i pv And reading in the voltage u of the photovoltaic port at the last moment of the photovoltaic system old And photovoltaic output power p old And then calculating to obtain the current photovoltaic array output power p pv ；
S202, judging u pv If u is greater than 5, if u pv <And 5, judging that the photovoltaic inverter works on the left side of the MPP at the moment, namely flag MPP is equal to-1, and converting the photovoltaic port voltage u at the moment into the photovoltaic port voltage u pv And photovoltaic output power p pv Assign u to old And p old Examination ofFinishing the measurement; if u pv >5, go to step S203;
s203, determines Δ u ═ u pv -u old If | is greater than 5, if Δ u<5, judging whether the cutting is straight cutting; if Δ u>5, go to step S204;
s204, judging k mpp ＝(u pv -u old )·(p pv -p old ) Whether greater than 0; if k is mpp <0, continuously judging the value of flagMPP; if k is mpp >0, reading in the current photovoltaic power instruction value p pv_ref And judges the value of FlagMPP.
Further, in step S204, if k is greater than k mpp <0, when flag MPP>0, make FlagAvF ═ 1, and let the photovoltaic port voltage u at this time pv And photovoltaic output power p pv Assign u to old And p old And the detection is finished; when flag MPP<0, reading the value of FlavaVF when the value of FlavaVF is<0, make FlagAvF ═ FlagAvF +1, and let the photovoltaic port voltage u at this moment pv And photovoltaic output power p pv Assign u to old And p old And the detection is finished; when FlagAvF is greater than or equal to 0, let u mpp ＝u pv 、i mpp ＝i pv 、p mpp ＝p pv FlagKno is equal to 1, FlagAvF is equal to-1, FlagMPP is equal to 1, and finally, the photovoltaic port voltage u at that time is obtained pv And photovoltaic output power p pv Assign u to old And p old And the detection is finished;
if k is mpp >0, when flag MPP<0, making FlagaAvF equal to-1, and changing the photovoltaic port voltage u at the moment pv And photovoltaic output power p pv Assign u to old And p old And the detection is finished; when flag MPP>0, read the value of FlagaAvF, if FlagaAvF<0, make FlagAvF ═ FlagAvF +1, and let the photovoltaic port voltage u at this moment pv And photovoltaic output power p pv Assign u to old And p old And the detection is finished; when FlagAvF is greater than or equal to 0, let u mpp ＝u pv 、i mpp ＝i pv 、p mpp ＝p pv FlagKno is 1, FlagAvF is-1, and FlagMPP is-1, which will be the endVoltage u of the photovoltaic port pv And photovoltaic output power p pv Assign u to old And p old And finishing the detection.
Specifically, step S3 specifically includes:
obtaining a reference voltage u pv_ref Judging whether the photovoltaic working mode value flag MPP is larger than 0;
if flag MPP<0, judging whether the flag Kno of the error switching is larger than 0 or not, and if so, judging whether the flag Kno is larger than 0>0, order u pv_ref ＝U MPP ，U MPP The voltage corresponding to the photovoltaic maximum power point is obtained, the flag flagRToL of the motion state of the photovoltaic working point is 1, and the switching is finished; if FlagKno<0, order u pv_ref ＝u pv_ref +c step ，c step The step parameter when the voltage of the photovoltaic port is increased from 0 is obtained, and the switching is finished;
if flag MPP>0, entering a power loop of the DC/DC converter to obtain an integrated value u of the power loop of the DC/DC converter pv_ref_ac ＝k i_dc_p ·p pv_err ，k i_dc_p As power loop integral coefficient, p pv_err Judging flagRToL as an error value between the reference power and the actual power; if FlagRToL>0, making flagRToL equal to 0, keeping the voltage command value of the photovoltaic port unchanged, and ending the switching; if FlagRToL<0, order u pv_ref ＝k p_dc_p ·p pv_err +u pv_ref_ac ，u pv_ref_ac Is the output value of the power-loop integral term, k p_dc_p And the switching is finished for the power loop proportional control coefficient.
Specifically, in step S4, the photovoltaic port voltage control command value u in_ref The method comprises the following specific steps:
wherein, U MPP Voltage, k, corresponding to the maximum power point of the photovoltaic p_dc_p Is the value, k, of the proportional controller of the power loop PI regulator i_dc_p Is the value of the integral controller of the power loop PI regulator, s is the integral element, p pv For photovoltaic output power, FlagMPP is lightThe volt operating mode value.
Another technical solution of the present invention is a non-energy-storage photovoltaic voltage type control system, including:
a conversion module for outputting a voltage u according to the d and q axes of the inverter d_ref 、u q_ref Obtaining modulation wave M under d and q axes by utilizing double closed-loop control of voltage and current d 、M q Then, the inverter three-phase modulation wave M is obtained by utilizing the inverter reference output voltage phase angle theta and through coordinate transformation a 、M b 、M c Then converting the voltage into a PWM duty ratio signal, and realizing double droop control of voltage and frequency at the direct current side by adopting a rear-stage inverter;
a detection module for detecting the working mode of the photovoltaic inverter and outputting a voltage u according to the sampled photovoltaic output pv And the photovoltaic output power p pv Obtaining a photovoltaic working mode value flag MPP and the motion condition of the current photovoltaic working point;
the judging module is used for judging whether the power P is required by the load according to the motion condition of the current photovoltaic working point obtained by the detecting module L Greater than the maximum photovoltaic power P MPP The photovoltaic inverter is enabled to work at the maximum power point through MPPT control, and the voltage of a photovoltaic port is controlled to be a command value u pv_ref The photovoltaic output voltage corresponding to the maximum power point; if the load demands power P L Less than the maximum photovoltaic power P MPP Switching the working mode according to the instruction value p of the output power of the photovoltaic array pv,ref Obtaining the photovoltaic output power p pv And calculating a photovoltaic port voltage control command value u by using the photovoltaic working mode value Flag pv_ref The photovoltaic output voltage corresponding to the maximum power point;
the control module is used for obtaining the photovoltaic output voltage u corresponding to the maximum power point according to the judgment module pv Photovoltaic port voltage control command value u pv_ref And the PWM duty ratio signal obtained by the conversion module is utilized to realize the power P required by the non-energy-storage photovoltaic inverter under the load L Greater than the maximum photovoltaic power P MPP And the load demand power P L Less than the maximum photovoltaic power P MPP Control strategies in two modes.
Compared with the prior art, the invention at least has the following beneficial effects:
according to the control method of the non-energy-storage photovoltaic voltage type, in the MPP running state, the photovoltaic inverter can simultaneously process power disturbance from a source side and a load side, the characteristic is applied to mode switching, and the cooperative work of a plurality of voltage control type photovoltaic inverters can be realized; even if the two-stage photovoltaic inverter is not supported by other energy sources, the two-stage photovoltaic inverter can actively adapt to the load requirement and actively support the power grid; the photovoltaic inverter can adjust the output power of the photovoltaic battery in real time without the support of other energy sources, match the load requirements under various complex conditions, realize reasonable distribution of power of each inverter in a photovoltaic isolated island, actively support the voltage frequency of an alternating current bus, and can simultaneously process power disturbance from both sides of a source load.
Furthermore, the inverter side is directly responsible for adjusting the direct current side capacitor voltage, and the inverter reference output voltage phase angle and the instruction value of the photovoltaic array output power are obtained according to the relation coefficient between the direct current voltage and the output frequency of the inverter side and the input power of the inverter, so that the photovoltaic inverter can respond to the photovoltaic output power and the fluctuation and randomness of the load power.
Furthermore, the d-axis voltage command value output by the inverter can be obtained through a traditional reactive voltage droop control strategy, and in order to improve the stability of a control system, virtual impedance is added into a d-axis voltage control loop and a q-axis voltage control loop to obtain the final d-axis voltage command value and the q-axis voltage command value output by the inverter.
Furthermore, the foregoing control steps are all performed in d and q axis coordinate systems, and after obtaining the d and q axis control command values, coordinate transformation from the d and q axis coordinate systems to a three-phase coordinate system is required to be performed on the d and q axis control command values to obtain modulated wave command values in the three-phase coordinate system, so as to implement control on the three-phase inverter.
Furthermore, the working area of the current photovoltaic inverter can be determined according to the result of comparison and calculation between the current photovoltaic output voltage and power value and the voltage power value at the previous moment, and a judgment basis is provided for selection of a photovoltaic inverter control strategy.
Further, the further detailed judgment step is beneficial to helping the photovoltaic inverter to deal with the environment and the condition change of the photovoltaic power supply, and the current working condition of the photovoltaic inverter is accurately judged so as to select a corresponding control strategy.
Further, the judging step uses a reasonable photovoltaic terminal voltage to detect the operation state of the photovoltaic inverter, and detection faults caused when the power characteristic curve of the photovoltaic cell changes due to environment are avoided through a hysteresis function FlagaAvF.
Furthermore, control strategies of the port voltage of the photovoltaic inverter under several working modes are provided.
Furthermore, two control strategies under two working modes are integrated, and a control instruction value of the voltage of the photovoltaic port is given.
In summary, the present invention can realize smooth mode switching when the photovoltaic power is insufficient, and the insufficient power can be borne by other photovoltaic inverters in the parallel system, thereby improving the flexibility of the photovoltaic inverter in the photovoltaic microgrid and the reliability of the photovoltaic inverter in future new energy application.
The technical solution of the present invention is further described in detail by the accompanying drawings and embodiments.
Drawings
Fig. 1 is a schematic diagram of a photovoltaic island microgrid circuit structure provided by the invention;
fig. 2 is a block diagram of a voltage-type control strategy for a two-stage photovoltaic inverter provided by the present invention;
FIG. 3 is a schematic diagram illustrating a photovoltaic operating mode detection technique provided by the present invention;
FIG. 4 is a schematic view of a photovoltaic working mode detection technique according to the present invention;
fig. 5 is a flow chart of switching the operating modes of the photovoltaic inverter provided by the present invention;
fig. 6 is a simulated waveform diagram of the pv inverter in normal and insufficient power modes, where (a) is the pv array and the inverter output power, (b) is the pv inverter output frequency, (c) is the pv array output voltage, (d) is the inverter side dc capacitor voltage, (e) is the MPP detection status flag, and (f) is the comparison of the pv output power command value and the actual value.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are some, not all, embodiments of the present invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
It will be understood that the terms "comprises" and/or "comprising," when used in this specification and the appended claims, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof.
It is also to be understood that the terminology used in the description of the invention herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used in the specification of the present invention and the appended claims, the singular forms "a," "an," and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise.
It should be further understood that the term "and/or" as used in this specification and the appended claims refers to and includes any and all possible combinations of one or more of the associated listed items.
Various structural schematics according to the disclosed embodiments of the invention are shown in the drawings. The figures are not drawn to scale, wherein certain details are exaggerated and possibly omitted for clarity of presentation. The shapes of various regions, layers and their relative sizes and positional relationships shown in the drawings are merely exemplary, and deviations may occur in practice due to manufacturing tolerances or technical limitations, and a person skilled in the art may additionally design regions/layers having different shapes, sizes, relative positions, according to actual needs.
Referring to fig. 1, the present invention provides a control method for a non-energy-storage photovoltaic voltage type, and the considered application background topology is specifically as follows: the photovoltaic power generation system comprises two photovoltaic inverters and no other energy storage or power generation equipment. Each inverter is of a two-stage conversion structure and comprises a DC/DC converter and a DC/AC converter, the output end of each inverter adopts an LCL filtering topological structure, each inverter is connected with an alternating current bus to transmit power to a load, and in order to verify the control strategy provided by the invention, other power supplies except photovoltaic power supplies are not adopted in a photovoltaic system; the photovoltaic inverter is enabled to work on the right side of a photovoltaic maximum power point by utilizing the unique characteristic of a photovoltaic curve, and the power of a photovoltaic output power tracking load is controlled, so that a photovoltaic system can independently run without an extra voltage source or an energy storage device, and smooth switching of control strategies of the photovoltaic under the conditions of different working areas and insufficient photovoltaic power can be met. The control method has good steady-state performance and dynamic performance and high engineering application value.
The invention discloses an energy-storage-free photovoltaic voltage type control method, which comprises the following steps of:
s1, adopting a rear-stage inverter to realize double droop control of voltage and frequency at the direct current side, ensuring the voltage at the direct current side to be constant and ensuring active power balance;
the control of the voltage and the frequency double droop at the direct current side specifically comprises the following steps:
s101, determining a direct-current side voltage reference value U of the inverter 0 Sag factor k d Virtual inertia J, synchronous angular frequency w ref Dc side capacitor C of inverter 0 And calculating a relation coefficient G between the input power of the photovoltaic array to the inverter and the DC side voltage of the inverter according to the relation coefficient G u And the relation coefficient G between the DC side voltage and the output frequency of the inverter w The calculation formula is as follows:
s102, obtaining a voltage reference value U of the direct current side of the inverter 0 And sampling the DC side voltage u of the inverter 0 Will u 0 And U 0 Making difference by using a relation coefficient G between the input power of the photovoltaic array to the inverter and the DC side voltage of the inverter u And the relation coefficient G between the DC side voltage and the output frequency of the inverter w And calculating to obtain a photovoltaic array output power instruction value p pv_ref And the phase angle theta of the reference output voltage of the inverter, the calculation formula is as follows:
s103, sampling the output voltage u of the inverter port abc Output current i abc Obtaining d-and q-axis voltages u through coordinate transformation d 、u q And a current i d 、i q Then, calculating to obtain real-time output reactive power Q of the inverter;
the expression of the abc/dq transformation block is as follows:
wherein i a 、i b 、i c Respectively the value i of the inverter output current in the abc three-phase stationary coordinate system d 、i q For the value of the inverter output current in dq synchronous rotating coordinate system, u a 、u b 、u c Respectively, the value u of the output voltage of the inverter in an abc three-phase static coordinate system d 、u q And the value theta of the output voltage of the inverter under the dq synchronous rotation coordinate system is the included angle between the d axis and the phase reference axis.
The reactive power is calculated as follows:
Q＝1.5×(v cq ·i cd -v cd ·i cq )
s104, according to the reactive power Q,Sag factor k d The rated voltage amplitude U of the alternating current bus of the inverter and the virtual impedance link are calculated to obtain the output reference voltage U of the d and q axes of the inverter d_ref 、u q_ref The calculation formula is as follows:
wherein L is v Is a virtual impedance.
S105, obtaining d-axis and q-axis reference output voltages u of the inverter d_ref 、u q_ref Obtaining modulation wave M under d and q axes by utilizing voltage current double closed-loop control d 、M q Then, the inverter three-phase modulation wave M is obtained by coordinate transformation by using the inverter reference output voltage phase angle theta obtained in the step S104 a 、M b 、M c Then converting the signal into a PWM duty ratio signal;
the calculation formula of the voltage outer ring control module for generating the current instruction is as follows:
wherein i d_ref And i d_ref Respectively outputting a reference value of active component and a reference value of reactive component, k p_du Value, k, of proportional controller for the active component of the output voltage of the inverter PI regulator i_du Value, k, of integral controller for the output voltage active component PI regulator of an inverter p_qu Value, k, of proportional controller for output voltage reactive component PI regulator of inverter i_qu Integrating controller value, u, for an inverter output voltage reactive component PI regulator d_ref For the active component reference value, u, of the output voltage of the inverter d Is a real component of the output voltage of the inverter u q_ref For the inverter to output a reference value of the reactive component of the voltage, u q And outputting a voltage reactive component for the inverter.
The calculation formula of the current inner loop control module for generating the modulation signal is as follows:
wherein M is d 、M q Generating a modulation command value for the d-axis current inner loop, a modulation command value for the q-axis current inner loop, k p_di 、k i_di The value of the proportional controller and the value of the integral controller, k, of the d-axis current inner loop PI regulator p_qi 、k i_qi The values of the proportional controller and the integral controller of the q-axis current inner loop PI regulator are respectively.
Will M d And M q Carrying out dq/abc inverse transformation to generate a driving PWM duty ratio signal, wherein the calculation formula is as follows:
referring to fig. 2, the DC/DC converter realizes droop control, and the inverter controls the DC side voltage to be constant. The power conduction mechanism of the synchronous machine is applied in the strategy, and the direct current capacitance in the two-stage photovoltaic inverter is higher than that of a conventional generator set of the photovoltaic inverter, such as a mechanical rotor. Therefore, the frequency of the output voltage of the inverter is determined by the voltage of the direct-current side capacitor, so that the output power of the photovoltaic array is controlled. The pre-DC/DC converter is directly responsible for droop control and frequency regulation, as is the prime mover, while the inverter is responsible for regulating the DC side capacitor voltage. The dc side voltage can regulate the output power of the photovoltaic as well as the output power of the inverter at the same time, which means that the source side and the load side can be regulated in power balance at the same time.
The inverter control strategy is specifically as follows:
firstly, according to the selected droop coefficient k d Virtual inertia J, synchronous angular frequency w ref Dc side capacitor C of inverter 0 Dc side voltage rating of inverter U 0 Calculating to obtain a control parameter G between the input power of the photovoltaic array to the inverter and the DC side voltage of the inverter u Control parameter between DC side voltage and output frequency of inverterG w (ii) a Obtaining the voltage u of the DC side of the inverter according to the sampling 0 Calculating the reference output power p of the photovoltaic power generation unit pv_ref And an inverter reference output voltage phase θ; sampling three-phase voltage u at AC bus side output by inverter abc And three-phase current i abc Calculating to obtain reactive power Q, obtaining rated voltage amplitude voltage U of the alternating current bus, and calculating to obtain reference output voltage amplitude U of the inverter dq (ii) a The obtained inverter reference output voltage phase theta and the inverter reference output voltage amplitude value U are obtained dq Synthesizing inner loop voltage command U ref 。
The control strategy of the DC/DC converter is specifically as follows:
the DC/DC converter ensures power balance for controlling the capacitance voltage at the direct current side, power, voltage and current three-closed-loop PI control is mainly adopted, the difference between the calculated photovoltaic power instruction value and the photovoltaic real-time power obtained by current sampling calculation is obtained through a PI regulator, the voltage instruction value is tracked through an inner-loop voltage and current loop based on the PI regulator, the duty ratio of the DC/DC converter is obtained, and tracking of the photovoltaic to the load power is completed.
S2, adopting a working mode detection method of the photovoltaic inverter;
firstly, sampling the output voltage u of the photovoltaic pv Output current i pv Calculating the output power p of the photovoltaic pv According to the sampled photovoltaic output voltage u pv And the photovoltaic output power p pv And calculating and judging the photovoltaic working mode to obtain the photovoltaic working mode value FlagMPP and the motion condition of the current photovoltaic working point.
Flag mpp is calculated as follows:
wherein u is old And p old Respectively, the photovoltaic port voltage and the photovoltaic power at the previous moment.
Referring to fig. 3, the detection principle of the photovoltaic working mode provided by the present invention specifically includes:
in order to realize source load power balance, the moving direction of the photovoltaic working point is determined by the load carried by the current photovoltaic inverter, and the controller records and updates the power value at the voltage monitoring point every monitoring step length deltav. Judging the current photovoltaic working area according to the current photovoltaic voltage and power value and the photovoltaic voltage and power value recorded by the controller at the last moment, and obtaining a corresponding photovoltaic working mode value flag MPP; according to the detection result of the photovoltaic working area, automatically selecting corresponding control feedback loops for the photovoltaic of different working areas, and calculating a photovoltaic port voltage control instruction value u pv_ref 。
Referring to fig. 4, the working mode detection process using the photovoltaic inverter specifically includes:
s201, sampling by the photovoltaic system to obtain the output voltage u of the current photovoltaic array pv Current i pv And reading in the voltage u of the photovoltaic port at the last moment of the photovoltaic system old And photovoltaic output power p old And then calculating to obtain the current photovoltaic array output power p pv ；
S202, judging u pv If u is greater than 5, if u pv <And 5, judging that the photovoltaic inverter works on the left side of the MPP at the moment, namely flag MPP is equal to-1, and converting the photovoltaic port voltage u at the moment into the photovoltaic port voltage u pv And photovoltaic output power p pv Assign u to old And p old And the detection is finished; if u pv >5, go to step S203;
s203, determines Δ u ═ u pv -u old If | is greater than 5, if Δ u<5, judging whether the cutting is straight cutting; if Δ u>5, go to step S204;
s204, judging k mpp ＝(u pv -u old )·(p pv -p old ) Whether greater than 0;
s2041, if k mpp <0, continuously judging the value of flagMPP;
s20411, if FlagMPP>0, making FlagaAvF equal to-1, and changing the photovoltaic port voltage u at the moment pv And photovoltaic output power p pv Assign u to old And p old And the detection is finished;
s20412, if FlagMPP<0, read the value of FlagaAvF, if FlagaAvF<0, make FlagAvF ═ FlagAvF + 1, and let the photovoltaic port voltage u at this moment pv And photovoltaic output power p pv Assign u to old And p old And the detection is finished; if FlagAvF is greater than or equal to 0, let u mpp ＝u pv 、i mpp ＝i pv 、p mpp ＝p pv FlagKno is equal to 1, FlagAvF is equal to-1, FlagMPP is equal to 1, and finally, the photovoltaic port voltage u at that time is obtained pv And photovoltaic output power p pv Assigned to u old And p old And the detection is finished;
s2042, if k mpp >0, reading in the current photovoltaic power instruction value p pv_ref And judges the value of FlagMPP.
S20421, if FlagMPP<0, making FlagaAvF equal to-1, and changing the photovoltaic port voltage u at the moment pv And photovoltaic output power p pv Assign u to old And p old And the detection is finished;
s20422, if FlagMPP>0, reading the value of FlagAvF, if FlagAvF<0, make FlagAvF ═ FlagAvF + 1, and let the photovoltaic port voltage u at this moment pv And photovoltaic output power p pv Assign u to old And p old And the detection is finished; if FlagAvF is greater than or equal to 0, let u mpp ＝u pv 、i mpp ＝i pv 、p mpp ＝p pv FlagKno is equal to 1, FlagAvF is equal to-1, FlagMPP is equal to-1, and finally, the photovoltaic port voltage u at that time is obtained pv And photovoltaic output power p pv Assign u to old And p old And the detection is finished.
The flag Kno flag bit is used for preventing false switching when the MPP is unclear; the FlagAvF flag bit serves as a hysteresis function to avoid false detection that may occur when the power characteristic of the photovoltaic array changes with the environment.
S3, adopting a mode switching method of the photovoltaic inverter when the power is insufficient;
firstly, a corresponding control strategy is selected through mode switching according to the detected photovoltaic working condition. If loadedPower demand P L Greater than the maximum photovoltaic power P MPP If so, the photovoltaic inverter is controlled to work at the maximum power point through MPPT; if the load demands power P L Less than the maximum photovoltaic power P MPP And (4) switching the working mode, and obtaining a photovoltaic output power instruction value in step S102.
Referring to fig. 5, when the power is insufficient, the photovoltaic operating mode switching process specifically includes:
obtaining a reference voltage u pv_ref Judging whether flag MPP is greater than 0;
if flag MPP<0, further judging whether the FlagKno is larger than 0, if so, determining whether the FlagKno is larger than 0>0, order u pv_ref ＝U MPP If FlagRToL is 1, the handover is finished; if FlagKno<0, order u pv_ref ＝u pv_ref +c step And the switching is finished.
If flag MPP>0, entering a power loop of the DC/DC converter to obtain u pv_ref_ac ＝k i_dc_p ·p pv_err And judging flagRToL. If FlagRToL>0, making flagRToL equal to 0, keeping the voltage command value of the photovoltaic port unchanged, and ending the switching; if FlagRToL<0, order u pv_ref ＝k p_dc_p ·p pv_err +u pv_ref_ac And the switching is finished.
Wherein u is pv_ref_ac Is a DC/DC converter power loop integral value; the flagRToL is a flag bit of the motion state of the photovoltaic working point, and when the flagRToL is 1, the flag RToL indicates that the motion state of the photovoltaic working point is just the process that the MPP moves from the right side to the left side of the MPP; c. C step Is the step parameter when the photovoltaic port voltage increases from 0.
And S4, the preceding stage Boost converter realizes the tracking of the specific photovoltaic power instruction value.
S401, after the photovoltaic power instruction value in the working mode is determined, a photovoltaic terminal voltage instruction value is obtained. If the photovoltaic inverter works at the maximum power point, the voltage control instruction value u of the photovoltaic port in_ref The photovoltaic voltage corresponding to the maximum power point; if the photovoltaic power instruction value p pv,ref If the power is less than the maximum power, obtaining a photovoltaic port voltage control instruction value u through power closed-loop control based on PI control in_ref The calculation formula is as follows:
s402, obtaining the duty ratio of a front-stage DC/DC converter of the photovoltaic inverter by utilizing voltage current double closed-loop control, and realizing that the photovoltaic inverter without energy storage is in P L >P MPP And P L <P MPP Control strategies in two modes.
In another embodiment of the present invention, an energy-free photovoltaic voltage control system is provided, which can be used to implement the above energy-free photovoltaic voltage control method.
The conversion module outputs a voltage u according to the d and q axes of the inverter d_ref 、u q_ref Obtaining modulation wave M under d and q axes by utilizing double closed-loop control of voltage and current d 、M q Then, the inverter three-phase modulation wave M is obtained by utilizing the inverter reference output voltage phase angle theta and through coordinate transformation a 、M b 、M c Then converting the voltage into a PWM duty ratio signal, and realizing double droop control of voltage and frequency at the direct current side by adopting a rear-stage inverter;
a detection module for detecting the working mode of the photovoltaic inverter and outputting a voltage u according to the sampled photovoltaic output pv And the photovoltaic output power p pv Obtaining a photovoltaic working mode value flag MPP and the motion condition of the current photovoltaic working point;
the judging module is used for judging whether the power P is required by the load according to the motion condition of the current photovoltaic working point obtained by the detecting module L Greater than the maximum photovoltaic power P MPP The photovoltaic inverter is enabled to work at the maximum power point through MPPT control, and the voltage of a photovoltaic port is controlled to be a command value u pv_ref The photovoltaic output voltage is used as the maximum power point; if the load requires power P L Less than the maximum photovoltaic power P MPP Switching the working mode according to the instruction value p of the output power of the photovoltaic array pv,ref Obtaining the photovoltaic output power p pv And calculating a photovoltaic port voltage control command value u by using the photovoltaic working mode value Flag pv_ref The photovoltaic output voltage corresponding to the maximum power point;
the control module is used for obtaining the photovoltaic output voltage u corresponding to the maximum power point according to the judgment module pv Photovoltaic port voltage control command value u pv_ref And the PWM duty ratio signal obtained by the conversion module is utilized to realize the power P required by the non-energy-storage photovoltaic inverter under the load L Greater than the maximum photovoltaic power P MPP And the load demand power P L Less than the maximum photovoltaic power P MPP Control strategies in two modes.
In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are some, but not all, embodiments of the present invention. The components of the embodiments of the present invention generally described and illustrated in the figures herein may be arranged and designed in a wide variety of different configurations. Thus, the following detailed description of the embodiments of the present invention, presented in the figures, is not intended to limit the scope of the invention, as claimed, but is merely representative of selected embodiments of the invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
In order to test the invention, a two-machine parallel simulation model as shown in fig. 1 was built in the PLECS. The power insufficiency caused by the power disturbance on both sides of the source load can be simulated by the change of the photovoltaic characteristic or the load. Where the maximum power of the PV1 PV array was reduced and increased at 2s and 4s, respectively, and loaded and unloaded at 6s and 8s, respectively, the simulation results are shown in fig. 6.
Before 2s, the two photovoltaic inverters can stably support the alternating current bus and supply power to the load, the load power is distributed through the droop coefficient, and the distributed power is 7.1kW because the droop coefficients of the two inverters are the same in the simulation. The MPP power (11.5kW for PV1 and 23kW for PV 2) is sufficient for the distributed power of each inverter, and as shown in fig. 6(a) and 6(d), the output power and voltage are stable and meet the design requirements.
And 2s, adopting the change of the output characteristic of the photovoltaic array. The maximum power of PV1 was reduced from 11.52kW to 4.5kW, which was 7.2kW less than its allocated power, resulting in power deficit. This condition may cause a failure of the pattern detection because the power of the same voltage point is different after the characteristic curve is changed, but this problem is solved by the failure detection method. Inverter PV1 switches rapidly to MPP mode, and insufficient power is compensated by PV 2. The PV1 operates in the MPP mode with the photovoltaic terminal voltage being the maximum value after the characteristic change and the output power being different from the command value, as shown in fig. 6(c) and 6 (f). Fig. 6(a), 6(b), and 6(d) show simulated waveforms of the power, frequency, and dc-side voltage of the pv inverter during switching, all of which can reach stable values quickly. At 4s, the maximum power of the PV1 photovoltaic array is increased from 4.5kW to 11.52kW, and the 7.2kW distributed by the load power is satisfied again, so that the normal working state is returned. And between 4s and 6s, the two photovoltaic inverters stably operate in a normal state.
At 6s the load increases and the maximum power of PV1 (11.5Kw) fails to meet the distributed power (16.1 Kw). Therefore, inverter PV1 operates in MPP mode, with inverter PV2 providing the remaining power of PV 1. The specific procedure first detects this condition using the mode detection method and changes the flag, and then the inverter PV1 operates in the MPP mode using the mode switching described above. As can be seen from the simulation results in fig. 6, the photovoltaic inverter can be smoothly switched to the MPP mode, and no interference is introduced during the switching. And when the load is reduced for 8s, the power meets the requirement of PV1 again, and the photovoltaic inverter returns to a normal operation state after detecting that the load power is reduced.
In summary, according to the control method and system for the non-energy-storage photovoltaic voltage type, in the island microgrid, the photovoltaic inverter can achieve reasonable power distribution for each inverter according to the load demand and the capacity of the inverter, and can actively adjust the voltage and the frequency of the alternating current bus. The photovoltaic mode detection and working mode switching strategy can well cope with source side power disturbance and load side power disturbance caused by photovoltaic randomness, smooth mode switching can be achieved when photovoltaic power is insufficient, the shortage power can be borne by other photovoltaic inverters in a parallel system, the flexibility of the photovoltaic inverters in the photovoltaic microgrid is improved, and the reliability of the photovoltaic inverter in future new energy application is improved.
The above-mentioned contents are only for illustrating the technical idea of the present invention, and the protection scope of the present invention is not limited thereby, and any modification made on the basis of the technical idea of the present invention falls within the protection scope of the claims of the present invention.
Claims (10)
1. A non-energy-storage photovoltaic voltage type control method is characterized by comprising the following steps:
s1, outputting voltage u according to d and q axes reference of inverter d_ref 、u q_ref Obtaining modulation wave M under d and q axes by utilizing double closed-loop control of voltage and current d 、M q Then, the inverter three-phase modulation wave M is obtained by utilizing the inverter reference output voltage phase angle theta and through coordinate transformation a 、M b 、M c Then converting the voltage into a PWM duty ratio signal, and realizing double droop control of voltage and frequency at the direct current side by adopting a rear-stage inverter;
s2, detecting the working mode of the photovoltaic inverter and outputting the voltage u according to the sampled photovoltaic pv And the photovoltaic output power p pv Obtaining a photovoltaic working mode value flag MPP and the motion condition of the current photovoltaic working point;
s3, according to the movement situation of the current photovoltaic working point obtained in the step S2, if the load needs power P L Greater than the maximum photovoltaic power P MPP The photovoltaic inverter is enabled to work at the maximum power point through MPPT control, and the voltage of a photovoltaic port is controlled to be a command value u pv_ref The photovoltaic output voltage corresponding to the maximum power point; if the load demands power P L Less than the maximum photovoltaic power P MPP Switching the working mode according to the instruction value p of the output power of the photovoltaic array pv,ref Obtaining the photovoltaic output power p pv And calculating a photovoltaic port voltage control command by using the photovoltaic working mode value FlagValue u pv_ref The photovoltaic output voltage corresponding to the maximum power point;
s4, obtaining the photovoltaic output voltage u corresponding to the maximum power point according to the step S3 pv Photovoltaic port voltage control command value u pv_ref And utilizing the PWM duty ratio signal obtained in the step S1 to realize the power P required by the non-energy-storage photovoltaic inverter under the load L Greater than the maximum photovoltaic power P MPP And the load demand power P L Less than the maximum photovoltaic power P MPP Control strategies in two modes.
2. The energy-free photovoltaic voltage type control method according to claim 1, wherein the step S1 specifically comprises:
s101, determining a direct-current side voltage reference value U of the inverter 0 Sag factor k d Virtual inertia J, synchronous angular frequency w ref Dc side capacitor C of inverter 0 And calculating a relation coefficient G between the input power of the photovoltaic array to the inverter and the DC side voltage of the inverter according to the relation coefficient G u And the relation coefficient G between the DC side voltage and the output frequency of the inverter w ；
S102, obtaining a DC side voltage reference value U of the inverter 0 And sampling the DC side voltage u of the inverter 0 Will u 0 And U 0 Making difference by using a relation coefficient G between the input power of the photovoltaic array to the inverter and the DC side voltage of the inverter u And the relation coefficient G between the DC side voltage and the output frequency of the inverter w And calculating to obtain a photovoltaic array output power instruction value p pv_ref Phase angle theta with the reference output voltage of the inverter;
s103, sampling the output voltage u of the inverter port abc Output current i abc Obtaining d-and q-axis voltages u through coordinate transformation d 、u q And a current i d 、i q Then, calculating to obtain real-time output reactive power Q of the inverter;
s104, according to the reactive power Q and the droop coefficient k d The inverter d is obtained by calculating the rated voltage amplitude U and the virtual impedance link of the AC bus of the inverter,q-axis output reference voltage u d_ref 、u q_ref ；
S105, obtaining d-axis and q-axis reference output voltages u of the inverter d_ref 、u q_ref Obtaining modulation wave M under d and q axes by utilizing voltage current double closed-loop control d 、M q Then, the inverter three-phase modulation wave M is obtained by coordinate transformation by using the inverter reference output voltage phase angle theta obtained in the step S104 a 、M b 、M c And then converted into a PWM duty signal.
3. The method according to claim 2, wherein in step S104, the inverter outputs reference voltage u on d and q axes d_ref 、u q_ref Comprises the following steps:
wherein L is v Is virtual impedance, U is rated voltage amplitude of AC bus of inverter, Q is reactive power, k d Is the sag factor, w ref For synchronous angular frequency, i d 、i q And outputting the value of the current under the dq synchronous rotation coordinate system for the inverter.
4. The non-energy-storage photovoltaic voltage type control method according to claim 2, wherein in step S105, the PWM duty cycle signal is:
wherein M is a 、M b 、M c For inverter three-phase modulated waves, θ is, M d 、M q A modulation command value is generated for the d-axis current inner loop.
5. The method for controlling the non-energy-storage photovoltaic voltage mode according to claim 1, wherein in step S2, the photovoltaic operation mode flag mpp is specifically:
wherein u is old And p old Respectively the photovoltaic port voltage and the photovoltaic power u at the previous moment pv For sampling the output voltage of the photovoltaic cell, p pv The photovoltaic output power.
6. The non-energy-storage photovoltaic voltage type control method according to claim 5, wherein the detecting the operation mode of the photovoltaic inverter is specifically:
s201, sampling by the photovoltaic system to obtain the output voltage u of the current photovoltaic array pv Current i pv And reading in the voltage u of the photovoltaic port at the last moment of the photovoltaic system old And photovoltaic output power p old And then calculating to obtain the current photovoltaic array output power p pv ；
S202, judging u pv If u is greater than 5, if u pv <And 5, judging that the photovoltaic inverter works on the left side of the MPP at the moment, namely flag MPP is equal to-1, and converting the photovoltaic port voltage u at the moment into the photovoltaic port voltage u pv And photovoltaic output power p pv Assign u to old And p old And the detection is finished; if u pv >5, go to step S203;
s203, determines Δ u ═ u pv -u old If | is greater than 5, if Δ u<5, directly cutting and quitting the judgment; if Δ u>5, go to step S204;
s204, judging k mpp ＝(u pv -u old )·(p pv -p old ) Whether greater than 0; if k is mpp <0, continuously judging the value of flagMPP; if k is mpp >0, reading in the current photovoltaic power instruction value p pv_ref And judges the value of FlagMPP.
7. The method according to claim 6, wherein in step S204, if k is greater than k mpp <0, when flag MPP>0, make FlagAvF ═ 1, and let the photovoltaic port voltage u at this time pv And photovoltaic output power p pv Assign u to old And p old And ending the detection; when flag MPP<0, read in the value of FlagaAvF when FlagaAvF<0, make FlagAvF ═ FlagAvF +1, and let the photovoltaic port voltage u at this moment pv And photovoltaic output power p pv Assign u to old And p old And the detection is finished; when FlagAvF is greater than or equal to 0, let u mpp ＝u pv 、i mpp ＝i pv 、p mpp ＝p pv FlagKno is equal to 1, FlagAvF is equal to-1, FlagMPP is equal to 1, and finally, the photovoltaic port voltage u at that time is obtained pv And photovoltaic output power p pv Assign u to old And p old And the detection is finished;
if k is mpp >0, when flag MPP<0, making FlagaAvF equal to-1, and changing the photovoltaic port voltage u at the moment pv And photovoltaic output power p pv Assign u to old And p old And the detection is finished; when flag MPP>0, read the value of FlagaAvF, if FlagaAvF<0, make FlagAvF ═ FlagAvF +1, and let the photovoltaic port voltage u at this moment pv And photovoltaic output power p pv Assigned to u old And p old And the detection is finished; when FlagAvF is greater than or equal to 0, let u mpp ＝u pv 、i mpp ＝i pv 、p mpp ＝p pv FlagKno is set to 1, FlagAvF is set to-1, FlagMPP is set to-1, and finally, the photovoltaic port voltage u at that time is set to 1 pv And photovoltaic output power p pv Assign u to old And p old And the detection is finished.
8. The energy-free photovoltaic voltage type control method according to claim 1, wherein the step S3 specifically comprises:
obtaining a reference voltage u pv_ref Judging whether the photovoltaic working mode value flagMPP is greater than 0;
if flag MPP<0, judging whether the flag bit FlagKno of the error switching is larger than 0, if so, judging whether the flag bit FlagKno is larger than 0>0, order u pv_ref ＝U MPP ，U MPP The voltage corresponding to the photovoltaic maximum power point is obtained, the flag flagRToL of the motion state of the photovoltaic working point is 1, and the switching is finished; if FlagKno<0, order u pv_ref ＝u pv_ref +c step ，c step The step parameter when the voltage of the photovoltaic port is increased from 0 is obtained, and the switching is finished;
if flag MPP>0, entering a power loop of the DC/DC converter to obtain an integral value u of the power loop of the DC/DC converter pv_ref_ac ＝k i_dc_p ·p pv_err ，k i_dc_p As power loop integral coefficient, p pv_err Judging flagRToL as an error value between the reference power and the actual power; if FlagRToL>0, making flagRToL equal to 0, keeping the voltage command value of the photovoltaic port unchanged, and ending the switching; if FlagRToL<0, order u pv_ref ＝k p_dc_p ·p pv_err +u pv_ref_ac ，u pv_ref_ac Is the output value of the power-loop integral term, k p_dc_p And the switching is finished for the power loop proportional control coefficient.
9. The non-energy-storage photovoltaic voltage type control method according to claim 1, wherein in step S4, the photovoltaic port voltage control command value u in_ref The method specifically comprises the following steps:
wherein, U MPP Voltage, k, corresponding to the maximum power point of the photovoltaic p_dc_p Is the value, k, of the proportional controller of the power loop PI regulator i_dc_p Is the value of the integral controller of the power loop PI regulator, s is the integral element, p pv For the photovoltaic output power, FlagMPP is the photovoltaic operating mode value.
10. An energy storage free photovoltaic voltage mode control system, comprising:
a conversion module for outputting a voltage u according to the d and q axes of the inverter d_ref 、u q_ref Obtaining d and q axes by utilizing double closed-loop control of voltage and currentModulated wave M of lower d 、M q Then, the inverter three-phase modulation wave M is obtained by utilizing the inverter reference output voltage phase angle theta and through coordinate transformation a 、M b 、M c Then converting the voltage into a PWM duty ratio signal, and realizing double droop control of voltage and frequency at the direct current side by adopting a rear-stage inverter;
a detection module for detecting the working mode of the photovoltaic inverter and outputting a voltage u according to the sampled photovoltaic output pv And the photovoltaic output power p pv Obtaining a photovoltaic working mode value flag MPP and the motion condition of the current photovoltaic working point;
the judging module is used for judging whether the power P is required by the load according to the motion condition of the current photovoltaic working point obtained by the detecting module L Greater than the maximum photovoltaic power P MPP The photovoltaic inverter is enabled to work at the maximum power point through MPPT control, and the voltage of a photovoltaic port is controlled to be a command value u pv_ref The photovoltaic output voltage corresponding to the maximum power point; if the load demands power P L Less than the maximum photovoltaic power P MPP Switching the working mode according to the instruction value p of the output power of the photovoltaic array pv,ref Obtaining the photovoltaic output power p pv And calculating a photovoltaic port voltage control command value u by using the photovoltaic working mode value Flag pv_ref The photovoltaic output voltage corresponding to the maximum power point;
the control module is used for obtaining the photovoltaic output voltage u corresponding to the maximum power point according to the judgment module pv Photovoltaic port voltage control command value u pv_ref And the PWM duty ratio signal obtained by the conversion module is utilized to realize the power P required by the non-energy-storage photovoltaic inverter under the load L Greater than the maximum photovoltaic power P MPP And the load demand power P L Less than the maximum photovoltaic power P MPP Control strategies in two modes.
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